People sell surplus camera licenses on eBay or Reddit (r/homelabsales). A single license often sells for $30–$40. If you need 4 cameras, total cost is ~$80 for a perpetual license—cheaper than two months of Ring subscription.
There is a misconception that ONVIF creates free licenses. It does not. synology surveillance station license free
Devices like door controllers or IP speakers often don't require a license. Mobile Devices: app to turn an old smartphone into a camera People sell surplus camera licenses on eBay or